Optical communication systems are at the core of modern telecommunications. They provide performance in terms of speed, capacity and reliability that make them an indispensable technology within the global communications infrastructure. To that end countless optical/electrical (opto-electronic) technologies have been developed to support the transmission and reception of optical signals through optical fiber channels. However, there has been, to this point, very little done in the field to investigate the effective deployment and configuration, of these new technologies, that would allow for the optimization of the end-to-end system performance in a closed loop configuration.
In conventional transmitter and receiver design great attention is paid to the configuration, setting, and control of optical and electronic components themselves. That is to say that the transmitter design is optimised with respect to its components and independently of the receiver and the effect of the fibre. Likewise the receiver is optimised with respect to its components independently of the transmitter and effect of the fibre. Thus no effort is made to optimise the end-to-end system performance by making setting/control choices taking the transmitter, receiver and fibre performances into consideration.
For example, in order to control the laser diode (LD) within the transmitter so that it has a stable optical output power while remaining accurately tunable in the spectrum of interest, an electronic closed-loop control mechanism is designed to control the temperature and bias (pump) current of the LD. However, that loop is a local loop within the transmitter, not a system loop. Thus, performance information from elsewhere in the optical communications system is not considered in the adjustment of the LD. Similar localized control loops exist all over the optical communication system.
However, as the art progresses and increased data-rates are demanded these localized control loops will not be able to provide a cost effective or efficient means for designing reliable high-speed optical communication links, and does not provide a means for tuning of the whole system to an optimal operating condition.
The above-discussed problems exist in both single-span and multiple span optical links. A single-span optical communication link can typically extend over distances of hundreds of meters up to about 80 km without the use of repeaters or amplifiers. Thus the transmitter is connected directly to the receiver by a fibre optic cable. Multiple transmissions may be combined through a multiplexer and the combined signal is transmitted to a receiving demultiplexer via a single fibre optic cable, without repeaters or amplifiers. Upon reception the combined signal is demultiplexed and routed to respective receivers. Multiple-span links then do include repeaters and/or amplifiers to boost the signal as it travels between its source and destination, whether the source provides a single channel or a combined signal formed by multiplexing multiple channels.